Physical information acquisition apparatus for driving physical information acquisition sensor control lines at multiple dividing points

ABSTRACT

A solid-state image sensor with one or more control lines driven at arbitrary dividing points along the control line.

RELATED APPLICATION DATA

This application is a division of U.S. patent application Ser. No.12/357,590, filed Jan. 22, 2009, which is a continuation of U.S. patentapplication Ser. No. 11/170,246, filed Jun. 29, 2005, the entirety ofwhich is incorporated herein by reference to the extent permitted bylaw. The present application also claims priority to Japanese PatentApplication Nos. 2004-195502, filed in the Japanese Patent Office onJul. 1, 2004, and 2005-175959, filed in the Japanese Patent Office onJun. 16, 2005, the entireties of both of which are incorporated byreference herein to the extent permitted by law.

BACKGROUND OF THE INVENTION

The present invention relates to a physical information acquisitionmethod, a physical information acquisition apparatus, and asemiconductor device. More particularly, the present invention relatesto a driving control technique in reading unit-element signals from unitelements, particularly suitable for use in a semiconductor device, suchas a solid-state image sensor including an array of unit elementssensitive to an electromagnetic wave such as light or radiation incidentfrom the outside and capable of outputting an electrical signalindicating a physical quantity distribution detected by the unitelements.

In various applications, to detect a physical quantity distribution, asemiconductor device is widely used which includes a linear array or amatrix array of unit elements (pixels) sensitive to a change in aphysical quantity such as a pressure or an electromagnetic wave such aslight or radiation incident from the outside.

For example, in video devices, a solid-state image sensor is used whichincludes an image sensor device of a CCD (Charge Coupled Device) type, aMOS (Metal Oxide Semiconductor) type, or a CMOS (ComplementaryMetal-Oxide Semiconductor) type to detect a change in a physicalquantity such as light (which is an example of an electromagnetic wave).

In computer devices, a fingerprint recognition device is used to acquirefingerprint information by detecting an image of a fingerprint based ona change in an electrical or optical characteristic associated with apressure. In these apparatus, a physical quantity distribution isconverted into an electrical signal by unit elements (pixels in the caseof a solid-state image sensor) and the resultant electrical signal isread out.

In some solid-state image sensors, an active pixel sensor is used inwhich a driving transistor for amplification is disposed in each imagesignal generation part that generates an image signal corresponding to asignal charge generated in a charge generation part. This structure isused in many CMOS solid-state image sensors.

In such an active solid-state image sensing apparatus, to read an imagesignal, unit pixels arranged in a pixel array part are sequentiallyselected by controlling addressing, and signals are read from therespective unit pixels. That is, the active solid-state image sensingapparatus is a solid-state image sensor of the address control type.

For example, in an active pixel sensor of the X-Y address type in whichunit pixels are arranged in the form of a matrix array, each pixel isconfigured to have an amplification capability using an active elementhaving a MOS structure (MOS transistor). In this structure, a signalcharge (photoelectrons) accumulated in a photodiode serving as aphotoelectric conversion device is amplified by the active element andread out as image information.

In the X-Y addressing solid-state image sensing device of this type, forexample, a pixel array part is formed using a large number of pixeltransistors arranged in the form of a two-dimensional matrix array.Accumulation of signal charges corresponding to incident light isstarted on a line-by-line (row-by-row) basis or a pixel-by-pixel basis,and a current or a voltage corresponding to the signal chargeaccumulated in each pixel is read sequentially from the respectivepixels by accessing the pixels by means of addressing. In solid-stateimage sensing devices of the MOS type (and of the CMOS type), theaddressing is performed, for example, such that pixels aresimultaneously accessed on a line-by-line basis and pixel signals areread from the accessed pixels, that is, pixel signals are read on aline-by-line basis from a pixel array part.

In some solid-state image sensing devices of this type, to adapt to thereading scheme of accessing the pixel array part on a line-by-line basisand reading pixels signals from the accessed line, analog-to-digitalconverters and/or other signal processing units are disposed forrespective vertical columns. This configuration is called a columnparallel arrangement. Of solid-state image sensing devices with a columnparallel arrangement, a solid-state image sensing device in which a CDSprocessor or a digital converter is disposed in each vertical columnsuch that pixel signals are sequentially read and output is called acolumn-type solid-state image sensing device.

As a result of reductions in size and cost of solid-state image sensingdevices such as CCD or CMOS image sensors, various kinds of videodevices using a solid-state image sensing device, such as a digitalstill camera for taking a still image, a portable telephone with acamera, and a video camera for taking a motion image, have come to bewidely used. CMOS image sensors can operate with less consumption powerand can be produced at a lower cost than CCD image sensors, and thusCMOS image sensors are expected to be widely used instead of CCD imagesensors.

In recent years, a great advance in semiconductor technology has beenmade, and, as a result, an increase in the number of pixels ofsolid-state image sensing devices has been achieved. For example,solid-state image sensing devices having several hundred pixels are nowavailable and used in high-resolution digital still cameras and movievideo cameras.

The increase in resolution results in an increase in the number of pixeltransistors. The increase in the number of pixel transistors and anincrease in the number of functions achieved by the capability ofaccessing arbitrary pixels result in an increase in the length ofcontrol lines for controlling reading of pixel signals. This causes anincrease in load imposed on drivers connected to the control lines andalso causes an increase in skew, which cannot be neglected.

For example, in CMOS image sensors, electrons generated as a result ofphotoelectric conversion are accumulated in each pixel, and pixelsignals are sequentially read from pixels in pixel columns (verticalcolumns) specified by address control signals output from a sensorcontrol unit (SCU).

More specifically, an address decoder is disposed in a vertical scanningcircuit located close to the pixel array part, and an address controlsignal is supplied from the address decoder to sequentially selectpixels. In accordance with the address control signal, the verticalscanning circuit supplies various kinds of control signals (genericallyit can be referred to as control signals) to a predetermined points ondrive control lines (particularly they can be referred to as originaldriving points) via driving buffers. And then, the control signals go topixel transistors, which are connected to respective driving points onthe drive control lines, through the drive control lines, therebyturning on/off the pixel transistor at the specified horizontal addressposition. Thus, the address decoder generates data indicating theaddress of a pixel to be selected.

Various control signals, by which to specify the horizontal addressposition, control turning on/off of the pixel transistor, aretransmitted via control signal lines, and pixel signals output frompixels in units of lines are sequentially transmitted in a horizontaldirection via a horizontal signal line (horizontal transfer line). Whenthere are a large number of pixels, these control signal lines andhorizontal signal line extend a long distance across the whole pixelarray part, and thus an interval between the original driving point andthe respective driving points where each pixel is connected get longer.Accordingly skew caused by the difference in locations of pixels alongthese control signal lines or the horizontal signal line becomes veryserious.

The skew can cause a reduction in a timing margin in an operation ofshading in a horizontal direction or in an operation of transferringdata to an amplifier at a following stage. Therefore, it is desirable tominimize the skew to as low a level as possible.

For example, a tree layout such as that shown in FIG. 10 is used toequally distribute a drive control signal (clock signal) in a sensor. Inthis layout, the overall skew of the circuit is dominated by a skew thatoccurs at a first stage having a longest interconnection. Thus, it isdesirable to minimize the skew at the first stage.

A widely used technique of driving the same line using one or twodriving buffers (pixel drivers) is to dispose one or two driving buffersat one or both ends of the line and drive the pixels using the drivingbuffers.

When pixels are driven from one side with one driving buffer (an exampleof driver unit) being connected to one end of the drive control lines,the distance between the driving buffer to the pixel varies greatlydepending on the location on the line. Thus, a difference in arrivaltime of a driving pulse (skew) occurs among pixels depending on thelocations of the pixels. That is, a difference in arrival time of thedriving pulse occurs between pixels located close to the driving bufferand pixels located far from the driving buffer. This can make itimpossible to read pixel signals or can cause shading.

When pixels are driven from both sides with two driving buffers (anexample of driver unit) being connected to both ends of the drivecontrol lines, the dependence of the distance from the driving buffer tothe pixel on the location on the line becomes smaller than in the casein which pixels are driven from one side. However, even when pixels aredriven from both sides, the dependence of the distance can be stilllarge. That is, when pixels are driven from both sides, it becomes moredifficult to read a signal from a pixel located at the center of theline as the number of pixels increases and/or as the signal reading rateincreases. This is a serious problem to be solved when the signalreading rate is increased.

SUMMARY OF THE INVENTION

The present invention provides a first physical information acquisitionmethod of reading unit-element signals from a semiconductor device, thesemiconductor device including unit elements arranged in a particularorder, each unit element having a unit-element signal generation partfor outputting a unit-element signal indicating a detected change in aphysical quantity, wherein a control line for driving unit elements toread unit-element signals from the respective unit elements is driven ata dividing point on the control line, and more preferably at a pluralityof dividing points on the control line.

The present invention provides a second a physical informationacquisition method, in which a control line is driven at an originaldriving point that results in a reduction in a maximum value of aproduct of load capacitance at an arbitrary driving point on the controlline and line resistance between the arbitrary driving point and adriver unit that is connected to the original driving point. Bydetermining the position at which to drive the control line, based onthe time constant, it is possible to select an optimum point at which todrive the control line even in a case in which line resistance and loadcapacitance are distributed non-uniformly.

The present invention also provides a physical information acquisitionapparatus including a drive control unit that drives a control line atan optimum point determined in the above-described manner.

The present invention also provides a semiconductor device including adrive control unit that drives a control line at an optimum pointdetermined in the above-described manner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is block diagram showing a CMOS solid-state image sensor (CMOSimage sensor), which is an example of a semiconductor device accordingto an embodiment of the present invention.

FIGS. 2 a-2 c are diagrams showing an example of a configuration of aunit pixel used in the solid-state image sensor shown in FIG. 1.

FIG. 3 is a diagram showing a skew reduction layout technique accordingto a first embodiment of the invention.

FIGS. 4A and 4B are diagrams showing a comparative example in which acontrol line is driven at only one end point thereof.

FIGS. 5A and 5B are diagrams showing a comparative example in which acontrol line is driven at both end points thereof.

FIG. 6 is a graph showing simulated skew that occurs when driving pointsare set at both end points according to a conventional technique andsimulated skew that occurs when a control line is driven using atwo-dividing-point equal driving method.

FIG. 7 is a diagram showing a skew reduction layout technique accordingto a second embodiment of the invention.

FIG. 8 is a diagram showing a skew reduction layout technique accordingto a third embodiment of the invention.

FIG. 9 is a diagram showing a skew reduction layout technique accordingto a fourth embodiment of the invention.

FIG. 10 is a diagram showing a tree-structure layout.

FIG. 11 is a diagram illustrating an example in which control lines aredriven at both end points thereof and at arbitrary points therebetween.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is described in further detail below withreference to embodiments in conjunction with the accompanying drawings.In embodiments described below, by way of example, a CMOS image sensordevice whose pixels are all formed of NMOS or PMOS devices is used toconstruct a solid-state image sensor of the X-Y address type.

Note that the image sensor device is not limited to the MOS-type imagesensor device, but the present embodiment and any other embodimentdescribed later may be applied to any semiconductor device including aone-dimensional or two-dimensional array of elements sensitive to anelectromagnetic wave incident from the outside, such as light orradiation.

<<Structure of Solid-State Image Sensor>>

FIG. 1 shows a CMOS solid-state image sensor (CMOS image sensor), whichis an example of a semiconductor device according to an embodiment ofthe present invention. This CMOS solid-state image sensor is also anexample of an electronic device according to an embodiment of thepresent invention.

Note that FIG. 1 shows an example of a circuit configuration, but thepurpose of FIG. 1 is not to define the location of each functional unit,and the manner in which driving buffers (pixel drivers) are locatedaccording to the present embodiment will be described in detail later.

The solid-state image sensor 1 has a pixel array part in which aplurality of pixels each including a photoelectric conversion devicesuch as a photodiode (which is an example of a charge generation part)for outputting an electronic signal corresponding to the intensity ofincident light are arranged along rows and columns (in the form of atwo-dimensional array). Voltage signals are output from respectivepixels and supplied to data processing units such as CDS (CorrelatedDouble Sampling) units and analog-to-digital converters (ADCs) disposedin a column-parallel fashion.

Herein, “disposing in a column-parallel fashion” implies that aplurality of CDS units and ADCs are disposed in substantially parallelat locations corresponding to the respective vertical columns alongwhich vertical signal lines 19 extend. The CDS units and ADCs may bedisposed only in an area adjacent to one side, which is perpendicular tothe columns (which is the lower side as viewed in FIG. 1), of the pixelarray part 10 or they may be disposed in areas adjacent to both sides ofthe pixel array part 10 such that some of the CDS units and ADSc aredisposed in one of the two areas (in the lower area in FIG. 1) and theremaining CDS units and ADSs are disposed in the other area (the upperarea in FIG. 1). In the latter case, it is desirable to divide thehorizontal scanning unit, which performs scanning (horizontal scanning)in the row direction, into two parts and dispose them in the tworespective areas adjacent to lower and upper sides of the pixel arraypart 10 such that they can operate independently.

The column type is a typical example in which CDS units and ADSs aredisposed in an area of an image sensing part, called a column area, in acolumn-parallel fashion at locations corresponding to respectivevertical columns such that signals are sequentially read via these CDSunits and ADSs to the outside. The manner of disposing CDS units andADSs is not limited to that used in the column type described above, butCDS units and ADSs may be disposed such that one CDS unit and one ADSare assigned to a predetermined number of (for example, two) adjacentvertical signal lines 19 (vertical columns), or such that one CDS unitand one ADS are assigned to every N (positive integer) vertical signallines 19 (vertical columns).

In the above-described configurations except for the column type, aplurality of vertical signal lines 19 (vertical columns) share one CDSunit and one ADS. To this end, a selection switch is disposed such thatpixels signals supplied from the plurality of signal lines 19 (verticalcolumns) of the pixel array part 10 are sequentially selected by theselection switch and the selected pixel signal is supplied to the oneCDS unit and one ADS. Depending on a process performed in followingstages, a memory for storing the output pixel signals is necessary.

In any case, using of one CDS unit and one ADS for a plurality ofvertical signal lines 19 (vertical columns) and performing of signalprocessing on the respective pixel signals after the pixel signals areread in units of pixel columns make it possible to construct each unitpixel in a simpler form than in the case in which similar signalprocessing is performed in each unit pixel, and thus it is possible toincrease the number of pixels of an image sensor, reduce the devicesize, and reduce the cost.

Because the plurality of signal processors disposed in thecolumn-parallel fashion can concurrently process pixel signals of onerow, the signal processors are allowed to operate at a lower speed thanan operating speed that is needed if the pixel signals are seriallyprocessed by only one CDS unit and one ADS disposed in an output circuitor disposed outside the device. This is advantageous in that the signalprocessors can operate with lower consumption power and a narrowerbandwidth, and the signal processors generate less noise. Conversely,when the same power consumption and the same bandwidth are allowed, itis possible to increase the overall operating speed of the sensor.

In the case of the column type, in addition to the advantages in termsof low power consumption, narrow bandwidth, and low noise obtained bythe low-speed operation, there is another advantage that no columnselection switch is needed. In the embodiments described below, theimage sensor is assumed to be of the column type unless otherwisestated.

As shown in FIG. 1, the solid-state image sensor 1 according to thepresent embodiment includes a pixel array part (image sensing part) 10,a drive control unit 7, a column processor 26 including a CDS unit 26 adisposed in an area adjacent to a lower side (as viewed in FIG. 1) ofthe pixel array part 10 and column switches (not shown), and an outputcircuit 28.

The column processor 26 functions as a main part of a normal imageprocessing system for performing signal processing associated withgeneration of a normal image based on an image signal acquired by thepixel array part 10.

As required, an AGC (Auto Gain Control) circuit having a signalamplification capability and/or an AD (Analog to Digital) converter maybe disposed in the same semiconductor area as the column processor 26,at a stage before or after the CDS unit 26 a. In the case in which theAGC circuit is disposed at the stage before the CDS unit 26 a, the AGCcircuit is of an analog type. On the other hand, when the AGC circuit isdisposed at the stage after the CDS unit 26 a, the AGC circuit is of adigital type. If n-bit digital data is simply amplified, there is apossibility that degradation occurs in halftone quality. To avoid theabove problem, it is desirable that an analog signal be amplified first,and then the resultant signal be converted into digital form.

The drive control unit 7 has a control circuit for sequentially readingan image signal from the pixel array part 10. More specifically, forexample, the drive control unit 7 includes a horizontal scanning circuit(column scanning circuit) 12 for controlling a column address and columnscanning, a vertical scanning circuit (row scanning circuit) 14 forcontrolling a row address and row scanning, and a communication/timingcontroller 20 having the capability of generating an internal clocksignal. The horizontal scanning circuit 12 includes a horizontal drivingcontroller (horizontal read scan circuit) for reading image informationfrom the column processor 26 or a processing unit 27.

The above-described elements of the drive control unit 7 are formed in asemiconductor area of single-crystal silicon or the like together withthe pixel array part 10 in an integrated form using a technique similarto that used in production of semiconductor integrated circuits, so asto obtain a solid-state image sensing device (image sensing device)which is an example of a semiconductor system according to theinvention.

In the present embodiment of the invention, the vertical scanningcircuit 14 includes a plurality of vertical scanning circuits (a firstvertical scanning circuit 14 a, a second vertical scanning circuit 14 b,and a third vertical scanning circuit 14 c in the example shown inFIG. 1) for sequentially selecting unit pixels 3 in the pixel array part10 and supplying an image signal read from each unit pixel 3 of thepixel array part 10 to the column processor 26, by driving the unitpixel 3 from both sides of the pixel array part 10 or from an arbitrarymiddle position of the pixel array part 10.

Typically, the first vertical scanning circuit 14 a and the secondvertical scanning circuit 14 b are used to drive control lines from theleft or right end of the pixel array part 10 and the third verticalscanning circuit 14 c is used to drive an arbitrary dividing point on acontrol line.

Although only some rows and columns are shown in FIG. 1 for the purposeof simplicity, an actual solid-state image sensor includes a greaternumber of rows and columns, and there are several ten to severalthousand unit pixels 3 in each row or column. Each unit pixel 3 includesa photodiode serving as a photosensor (a charge generation part) and apixel amplifier including a semiconductor element (for example, atransistor) for amplification.

Each unit pixel 3 is connected to the vertical scanning circuit 14 via arow control line 15 for selecting a row and to the column processor 26for outputting a normal image via a vertical signal line 19. Note thatthe term “row control line 15” generically denotes all control linesextending from the vertical scanning circuit 14 to the pixels.

The communication/timing controller 20 controls the timing of drivingpulses output from the plurality of vertical scanning circuits 14 (14 a,14 b, and 14 c) such that the driving pulses are output at substantiallythe same time from the output terminals of the respective verticalscanning circuits 14 to the row control lines 15.

The vertical scanning circuits 14 (14 a, 14 b, and 14 c) and thehorizontal scanning circuit 12 each have a decoder and start readingpixel signals to be processed in response to a control signal CN1 (CN1a, CN1 b, or CN1 c) or CN2 supplied from the communication/timingcontroller 20. Therefore, various kinds of drive control pulses (such asa reset pulse RST, a transfer control pulse TX, a DRN control pulse DRN,and a vertical selection pulse SEL) for driving unit pixels 3 aretransmitted via each row control line 15.

The vertical scanning circuits 14 (14 a, 14 b, and 14 c) and thecommunication/timing controller 20 form a unit-element signal selectioncontroller (vertical drive controller) that specifies positions ofrespective unit pixels 3 to be processed and reads pixels signals fromthe respective unit pixels 3 at the specified positions to the columnprocessor 26.

The communication/timing controller 20 includes (although not shown) afunctional block serving as a timing generator TG (which is an exampleof a read address controller) that supplies a clock signal or timingpulses needed in operations of various parts and also includes afunctional block serving as a communication interface that receives amaster clock CLK0 via a terminal 5 a and data DATA indicating anoperation mode or the like via a terminal 5 b and outputs data includinginformation associated with the solid-state image sensor 1.

For example, a horizontal address control signal is supplied to ahorizontal decoder, and a vertical address control signal is supplied toa vertical decoder, and each decoder selects a row or a column inaccordance with the received horizontal or vertical address controlsignal.

To achieve high-speed reading of image signals from the unit pixels 3disposed in the two-dimensional matrix form, it is desirable to scanunit pixels 3 such that the unit pixels 3 are accessed in units of rows,and analog pixel signals output in the column direction from theaccessed unit pixels 3 are acquired, and then the acquired analog pixelsignals are output in the row direction to the external circuit. Insteadof scanning unit pixels 3 in the above-described manner, an arbitraryunit pixel 3 may be directly accessed by specifying its address to readnecessary information from the specified unit pixel 3.

The vertical scanning circuit 14 supplies a pulse to select a row of thepixel array part 10. More specifically, each of a first verticalscanning circuit 14 a, a second vertical scanning circuit 14 b, and athird vertical scanning circuit 14 c has a vertical driving circuit 144including a vertical decoder (vertical shift register) 142 thatspecifies the vertical position of a row from which to read pixelsignals, and also including a driving buffer (pixel driver) (not shown)that buffers the signal received from the vertical decoder 142 andsupplies a drive control pulse to a row control line 15 corresponding tothe row specified by the vertical decoder 142 to drive unit pixels 3 onthe specified row. The vertical decoder 142 also serves to select a rowin an electronic shuttering operation in addition to selection of a rowin a signal reading operation.

The horizontal scanning circuit 12 sequentially selects functional partsof the column processor 26 in synchronization with a low-speed clockCLK2 and supplies signals output from the respective functional parts ofthe column processor 26 to a horizontal signal line (horizontal outputline) 18. The horizontal scanning circuit 12 includes a horizontaldecoder 122 that specifies the location in the horizontal direction of acolumn from which to read a pixel signal (that is, specifies a CDS unit26 a in the column processor 26) and also includes a horizontal drivingcircuit 124 that transmits the signal output from the column processor26 to the horizontal signal line 18 in accordance with the read addresssupplied from the horizontal decoder 122.

In the case in which the pixel signals are converted into digital formby the column processor 26 (and more particularly by the respective CDSunits 26 a), as many horizontal signal lines 18 are needed as the numberof bits n (positive integer) dealt with by the column processor 26. Forexample, when n=10, ten horizontal signal lines 18 are needed.

In the solid-state image sensor 1 constructed in the above-describedmanner, image signals output from unit pixels 3 in the respectivevertical columns are supplied to the CDS unit 26 a of the columnprocessor 26 via vertical signal lines 19.

In the normal image generation/output system, the image signals from thepixel array part 10 are transmitted to the column processor 26 locatedon a lower side, as viewed in FIG. 1, of the pixel array part 10. Inthis transmission of the image signals from the pixel array part 10, allpixels in one horizontal row are simultaneously selected by the verticalscanning circuit 14 and the pixel signals of the respective verticalcolumns are simultaneously output in parallel. That is, the pixelsignals are output in a column-parallel mode.

The CDS unit 26 a of the column processor 26 performs a CDS process onthe image signal in a voltage form input via the vertical signal line19. More specifically, a signal level (indicating a noise level)obtained immediately after a pixel is reset is subtracted from a pixelsignal Vsig (indicating the intensity of incident light) therebyremoving a noise signal component such as fixed pattern noise (FPN) orreset noise from the pixel signal.

After the CDS process is performed by the column processor 26, theresultant image signal is transmitted to the horizontal signal line 18via a horizontal selection switch (column switch) driven by thehorizontal selection signal supplied from the horizontal scanningcircuit 12 and further transmitted to the output circuit 28. Theabove-described process performed in the normal mode is known (a furtherdetailed description may be found, for example, inISSCC/2000/SESSION6/CMOS IMAGE SENSORS WITH EMBEDDED PROCESSORS/6.1(2000 IEEE International Solid-State Circuits Conference)), and thus afurther detailed description thereof is omitted.

In the solid-state image sensor 1 configured in the above-describedmanner, the respective pixels are driven by the first vertical scanningcircuit 14 a, the second vertical scanning circuit 14 b, and the thirdvertical scanning circuit 14 c such that image signals output frompixels in respective vertical columns are supplied on a row-by-row basisfrom the pixel array part 10, in which photosensors serving as chargegeneration parts are arranged in the form of the matrix array, to thecolumn processor 26 and output to the external circuit at a normal framerate.

As a result, one frame of image composed of a set of pixel signalsoutput from the respective photosensors (photoelectric conversiondevices such as photodiodes) arranged in the form of the matrix array inthe pixel array part 10 is output as an image signal S0 from the outputcircuit 28 to the external circuit 100.

The external circuit 100 includes an analog-to-digital (A/D) converterfor converting the analog image signal S0 output from the output circuit28 into digital image data D0, and also includes a digital signalprocessor (DSP) for performing digital signal processing on the digitalimage data output from the A/D converter. The digital signal processorperforms color separation on the image data and further performs othersignal processing the image data RGB thereby generating image data RGBrepresenting R (red), G (green), and B (blue) image components to beoutput to a monitor. The digital signal processor has a functional blockfor compressing image data to be stored on a storage medium.

The external circuit 100 also includes a digital-to-analog (D/A)converter for converting digital image data output from the digitalsignal processor into an analog image signal. The image signal outputfrom the D/A converter is supplied to a display device such as a liquidcrystal monitor. A user can perform various operations while viewing theimage displayed on the display device.

Although in the present embodiment, the solid-state image sensor 1,which is an example of a physical information acquisition apparatus (inthe broad sense) according to the invention, is realized by forming, ona single circuit board or a single semiconductor substrate, the pixelarray part 10 that is the main part of the image sensor that is anexample of a semiconductor device, and the physical informationacquisition apparatus (in the narrow sense) including the drive controlunit 7 that drives the pixel array part 10 and also including the columnprocessor 26 that performs the signal processing on the image signaloutput from the pixel array part 10, the solid-state image sensor 1 maybe configured in various other ways. For example, the pixel array part10 and the other parts may be formed separately. In this case, thephysical information acquisition apparatus is configured using the drivecontrol unit 7 and the column processor 26.

<<Pixel Structure>>

FIG. 2 shows an example of a structure of a unit pixel 3 and arelationship of the driver unit and pixel transistors used in thesolid-state image sensor 1 shown in FIG. 1. In the example shown in FIG.2, the structure of each unit pixel (pixel cell) 3 in the pixel arraypart 10 is similar to that of a common CMOS image sensor, and each unitpixel 3 is configured with four transistors. Note that the configurationof the unit pixel 3 is not limited to the 4-transistor configurationemployed herein, but other configurations such as a 3-transistorconfiguration disclosed in Japanese Patent No. 2708455 may also beemployed, as long as the configuration of the unit pixel 3 allows it toform a CMOS image sensor array.

As for the in-pixel amplifier, for example, a floating diffusionamplifier may be used. More specifically, for example, a 4-transistorconfiguration widely used in CMOS sensors can be realized using a readselection transistor that is an example of a charge reading part(transfer gate/read gate) connected to a charge generation part, a resettransistor that is an example of a reset gate, a vertical selectiontransistor, and an amplification transistor in the form of a sourcefollower that is an example of a detection element for detecting avoltage change of the floating diffusion layer.

For example, in the 4-transistor configuration shown in FIG. 2(A), theunit pixel 3 is formed using a charge generation part 32 for convertingincident light into a charge and storing the resultant charge, a readselection transistor (transfer transistor) 34 that is connected to thecharge generation part 32 and that is an example of a charge readingelement (transfer gate/read gate), a reset transistor 36 that is anexample of a reset gate, a vertical selection transistor 40, and anamplification transistor 42 in the form of a source follower that is anexample of a detection element for detecting a voltage change of afloating diffusion layer 38.

This unit pixel 3 includes an image signal generation part 5 in the formof a floating diffusion amplifier (FDA) formed of the floating diffusionlayer 38 that is an example of a charge injection part having a chargeaccumulation function. The floating diffusion layer 38 is a diffusionlayer having parasitic capacitance.

The read selection transistor (second transfer element) 34 is driven bya transfer driving buffer 250 via a transfer line (read selection lineTX) 55. The reset transistor 36 is driven by a reset drive buffer 252via a reset line (RST) 56. The vertical selection transistor 40 isdriven by a selection drive buffer 254 via a vertical selection line(SEL) 52. These drive buffers are independently driven by the firstvertical scanning circuit 14 a or the second vertical scanning circuit14 b.

The source of the reset transistor 36 in the image signal generationpart 5 is connected to the floating diffusion layer 38, and the drainthereof is connected to the power supply VDD. To the gate (reset gateRG) of the reset transistor 26, a reset pulse RST is input via a resetdriving buffer. The reset transistor 36 serves to reset the voltage ofthe output circuit 28.

The drain of the vertical selection transistor 40 is connected to thesource of the amplification transistor 42, the source thereof isconnected to the pixel line 51, and the gate (vertical selection gateSELV) thereof is connected to the vertical selection line 52. Theconnection is not limited to this example, but the electrodes of thevertical selection transistor 40 may be connected in other ways. Forexample, the drain of the vertical selection transistor 40 may beconnected to the power supply VDD, the source may be connected to thedrain of the amplification transistor 42, and gate may be connected tothe vertical selection line 52.

A vertical selection signal SEL is applied to the vertical selectionline 52. The gate of the amplification transistor 42 is connected to thefloating diffusion layer 38, the drain thereof is connected to the powersupply VDD, and the source thereof is connected to the pixel line 51 viathe drain of the vertical selection transistor 40 and further to thevertical signal line 19.

In this 4-transistor configuration, because the floating diffusion layer38 is connected to the gate of the amplification transistor 42, theamplification transistor 42 outputs a voltage signal corresponding tothe voltage of the floating diffusion layer 38 (hereinafter, referred toas an FD voltage) to the vertical signal line 53 (19) via the pixel line51.

The reset transistor 36 resets the floating diffusion layer 38. The readselection transistor (transfer transistor) 34 transfers the signalcharge generated in the charge generation part 32 to the floatingdiffusion layer 38. To select one of many pixels connected to thevertical signal line 19, a vertical selection transistor 40 connected toa pixel to be selected is turned on while maintaining other verticalselection transistors 40 in the off state. As a result, the selectedpixel is connected to the vertical signal line 19 and a signal outputfrom the selected pixel is output via the vertical signal line 19.

On the other hand, if the 3-transistor configuration using a chargegeneration part and three transistors is employed, it is possible toreduce the area occupied by the transistors in the unit pixel 3 and thusit is possible to reduce the total size of the unit pixel 3 (refer to,for example, Japanese Patent No. 2708455).

For example, as shown in FIG. 2B, a unit pixel 3 can be formed in a3-transistor configuration using a charge generation part 32 (forexample, a photodiode) for generating a signal charge corresponding toincident light by means of a photoelectric conversion, an amplificationtransistor 42 connected to a drain line (DRN), for amplifying the signalvoltage corresponding to the signal charge generated by the chargegeneration part 32, and a reset transistor 36 for resetting the chargegeneration part 32. A read selection transistor (transfer gate) 34,which is driven by a vertical scanning circuit 14 (not shown) via atransfer line (TRF) 55, is disposed between the charge generation part32 and the gate of the amplification transistor 42.

The gate of the amplification transistor 42 and the source of the resettransistor 36 are connected to the charge generation part 32 via theread selection transistor 34, and the drain of the reset transistor 36and the drain of the amplification transistor 42 are connected to thedrain line. The source of the amplification transistor 42 is connectedto the vertical signal line 53.

The read selection transistor 34 is driven by the transfer drivingbuffer 250 via the transfer line 55. The reset transistor 36 is drivenby the reset driving buffer 252 via the reset line 56.

The transfer driving buffer 250 and the reset driving buffer 252 operatewith a voltage swing between a reference voltage of 0 V and a powersupply voltage. Thus, a low-level voltage supplied to the gate of theread selection transistor 34 in the pixel is equal to 0 V.

In this unit pixel 3 with the 3-transistor configuration, as in the unitpixel 3 with the 4-transistor configuration, because the floatingdiffusion layer 38 is connected to the gate of the amplificationtransistor 42, a signal output from the amplification transistor 42 tothe vertical signal line 53 has a voltage corresponding to the voltageof the floating diffusion layer 38.

The reset line (RST) 56 connected to the reset transistor 36 extends inthe row direction. The drain line (DRN) 57 is connected in common toalmost all pixels. The drain line 57 is driven by a drain driving buffer(hereinafter, referred to as a DRN driving buffer) 240. The resettransistor 36 is driven by the reset driving buffer 252 to control thevoltage of the floating diffusion layer 38.

Although in FIG. 2(B), the drain line 57 is divided in the rowdirection, drain lines 57 in a row are actually connected in common toeach other such that all pixels in the row are simultaneously driven.The signal charge generated by the charge generation part 32(photoelectric conversion device) is transferred to the floatingdiffusion layer 38 via the read selection transistor 34.

In the 3-transistor configuration, unlike the 4-transistorconfiguration, the unit pixel 3 does not have the vertical selectiontransistor 40 connected in serial to the amplification transistor 42.The selection of one of many pixels connected to the vertical signalline 53 is performed not by turning on the selection transistor but bycontrolling the FD voltage. The FD voltage is normally at a low level.If the FD voltage of the pixel to be selected is raised to a high level,the signal output from the selected pixel is supplied to the verticalsignal line 53. Thereafter, the FD voltage of the selected pixel isreturned to the low level. This process is simultaneously performed forall pixels in one row.

More specifically, the FD voltage is controlled as follows. 1) To raisethe FD voltage of a row to be selected to the high level, the drain line57 is raised to the high level to raise the FD voltage to the high levelvia the reset transistors 36 in the row to be selected, and 2) the FDvoltage of the selected row is returned to the low level by lowering thedrain line 57 to the low level thereby lowering the FD voltage to thelow level via the reset transistors 36 in the row to be selected.

In the above-described operation, the load that is imposed on the draindriving buffer 240 when the drain driving buffer 240 drives the drainline 57 becomes greater than the load that is imposed on the transferdriving buffer 250 when the transfer driving buffer 250 drives thetransfer gate line 55 that is another driving line and greater than theload that is imposed on the reset driving buffer 252 when the resetdriving buffer 252 drives the reset gate line 56, and thus the skewdepending on the location on the line acting as the load becomes greaterthan the skew on the transfer gate line 55 or the reset gate line 56.

Each transistors 34, 36 and 40, which are included in unit pixel 3, aredriven by the driving buffer through the drive control lines 52, 55, 56and 57.

Drive control pulses are transmitted to the drive control line with thedriver unit being connected to the predetermined points of the drivecontrol line, as described in FIG. 2( c). And then, the drive controlpulses reach the pixel transistors, which are connected to arbitrarypoints on the drive control line, through the drive control line. Thedrive control line as a whole is an object of driving by the driver unitand so all the points on the drive control line can be the drivingpoints.

<<Concept of Improving Method>>

In the present embodiment, when a pixel signal is read by driving eachunit pixel 3 of the pixel array part 10, a control line is driven at aparticular point (or at a plurality of points) in a particular range ofthe control line include in the substantially effective area of thepixel area 10, in which to suppress the skew by a driving buffer (driverunit) so that the load imposed by pixels on the driving buffer isreduced and becomes uniform (the dependence of the location on the loadis reduced).

To achieve the above purpose, the control line is driven by a drivingbuffer (pixel driver) at an arbitrary dividing point (and morepreferably, at a plurality of dividing points). As required, the controlline is also driven at one or both ends of the control line.

To drive the control line at a dividing point, a driving buffer isconnected, at the arbitrary dividing point, to the control lineextending in the pixel array part 10 and a drive control pulse issupplied from the driving buffer over the control line at the sametiming as that of a drive control pulse supplied from one or both endpoints of control line. The dividing point on the drive control line,which is connected to the driver unit is the original driving point.

The control line the skew along which is to be suppressed and thedriving buffers are disposed so as to make the greatest value ofproducts of the load capacitance and the line resistance between thedividing point (original driving point) and an arbitrary driving pointon the drive control line within the effective range in which the skewis to be suppressed, smaller than on the driving method of the relatedart (one-end driving or both-ends driving) and preferably to make amaximum value of a products local minimum or substantially localminimum. The details of the technique are described below with referenceto specific examples.

First Embodiment

FIG. 3 shows a manner in which driving buffers are disposed so as toreduce skew (hereinafter, the technique will be referred to as a skewreduction layout technique) according to a first embodiment of theinvention. FIG. 4 shows a comparative example in which driving isperformed at one end, and FIG. 5 shows another comparative example inwhich driving is performed at both ends.

When a vertical driving circuit 144 (that is, a driving buffer BF) isdisposed at only one side of the pixel array part 10 as in the case ofthe configuration shown in FIG. 4(A), the load increases as the numberof pixels is increased to achieve higher resolution. The increase in theload results in an increase in the difference in reading time between apixel located close to the driving buffer and a pixel located far fromthe driving buffer. This can make it difficult to correctly read pixelsignals, and can cause shading or noise.

If the total line resistance is denoted by R and the total parasiticcapacitance is denoted by C as shown in FIG. 4(B), the time constant τafor a point farthest from the driving point when driving is performed atone end is given by equation (1).[Formula 1]τa=RC  (1)

The “farthest point” refers to a point on a control line the distancefrom which to a original driving point at which a driving buffer isconnected to the control line is greatest. When the line resistance andthe load capacitance are uniformly distributed, the time constant (lineresistance×load capacitance) becomes greatest at the farthest point, andthe greatest value of the time constant is minimized by properlyselecting the point at which the control line is driven.

One technique to ease the problem described above is, as shown in FIG.5(A), to dispose vertical driving circuits 144 (driving buffers) on leftand right sides of the pixel array part 10 and drive a control lineconnected to pixels from both sides of the pixel array part 10 therebyreducing the load imposed on each driving buffer.

In this case, as shown in FIG. 5(B), if the total line resistance isdenoted as R and the total parasitic capacitance is denoted as C, theline resistance and the parasitic capacitance at a point (at the centerof the control line) farthest from both driving points (end points) arerespectively given by R/2 and C/2, and thus the time constant τb at thepoint farthest from the driving points when the control line is drivenat both ends is given by equation (2). Therefore, theoretically, theskew can be reduced to ¼ of that which occurs when the control line isdriven at one end.[Formula 2]τb=R/2×C/2=RC/4  (2)

However, when the control line is driven at both ends, a pixel locatedat the center of the control line is driven with a greatest delay,although the delay is smaller than the delay that occurs when thecontrol line is driven at one end. This is a serious problem to besolved when it is needed to read pixel signals at a higher speed.

In view of the above, in the first embodiment, as shown in FIG. 3,instead of driving the control line at both ends, the control line isdriven at two dividing points on the control line whose distance from acloser end of the range in which skew is to be minimized is equal to ¼of the total length of the range. Hereinafter, this driving method willbe referred to as a two-dividing-point equal driving method.

In this driving method, if the total line resistance is denoted as R andthe total parasitic capacitance is denoted as C, the line resistance andthe parasitic capacitance at points farthest from the respective drivingpoints (at both ends of the control line and at the center of thecontrol line, in this specific example) are respectively given by R/4and C/4, and thus the time constant τc at the points farthest from thedriving points in the “two-dividing-point equal driving method” is givenby equation (3). From equation (3), it can be seen that the timeconstant is ¼ of that in the both-end driving method and 1/16 of that inthe one-end driving method.[Formula 3]τC=R/4×C/4=RC/16  (3)

That is, when original driving points are set at points whose distancefrom a closer end of a line is ¼ of the total length of the line, thetheoretical skew is reduced to 1/16 of that in the one-end drivingmethod shown in FIG. 4 and to ¼ of that in the both-end driving methodshown in FIG. 5.

The driving buffers for driving the control line at dividing points donot necessarily need to be disposed within the vertical scanning circuit14 c. More preferably, they may be disposed in at least one of thevertical scanning circuits 14 a and 14 b, and the dividing points may beconnected to the respective driving buffers via connection linesextending in parallel with the metal control line toward one or bothends of the control line.

This is because when a 2-dimensional sensor including a plurality ofcontrol lines extending in the row direction is driven, if drivingbuffers are disposed in the third vertical scanning circuit 14 c locatedin the area adjacent to the upper side of the pixel array part 10, thedistance from the driving buffers to the row varies depending on therow, and thus characteristics vary depending on the row. That is, newskew occurs. On the other hand, in the case in which driving buffers aredisposed in the vertical scanning circuits 14 a and 14 b, and thedriving points are connected to the respective driving buffers viaconnection lines extending in parallel with the control lines, all rowshave equal characteristics.

In FIG. 11, there is illustrated an example of an additional drivingcircuit 14C which generates driving control pulses for driving thecontrol lines at arbitrary dividing points located at other than theends of the control lines. As illustrated, each control line is drivenat an additional two locations as determined by the calculationsdiscussed herein. When a control line is driven by driving controlpulses 15 at both ends, it is also driven at the arbitrary dividingpoints by the driving control pulses 15. This is discussed in connectionwith the embodiment of FIG. 8.

As also illustrated, a signal path for a given driving control signal15C can be coupled to multiple similar control lines, i.e. a similarcontrol line in each row.

Of course, the control lines need not be driven at the ends thereof, asdiscussed in connection with FIGS. 3 and 7.

FIG. 6 shows simulated skew at nodes b0 and b1 that occur when originaldriving points are set at both end points according to the conventionaltechnique and simulated skew at nodes c0 and c1 that occur when originaldriving points are set at two dividing points.

In the simulation, parameters were set as follows.

1) Total line resistance: R=1.3 kΩ

2) Total parasitic line capacitance: C=1.5 pF

3) Driving buffer size: properly set to be capable of driving the line.

As can be seen from FIG. 6, the skew between nodes b0 and b1 is 250 ps,and the skew between nodes c0 and c1 is 70 ps which is ¼ of that betweennodes b0 and b1 (when the skew is measured at 0.5 Vdd). This means that,theoretically, the skew can be reduced by employing thetwo-dividing-point equal driving method.

Second Embodiment

FIG. 7 shows a skew reduction layout technique according to a secondembodiment of the invention. In this second embodiment, two ends of thecontrol line are not used as original driving points, but originaldriving points are set at three dividing points of the control line suchthat points farthest from the respective driving points within the rangein which skew is to be suppressed are distributed substantially equally.Hereinafter, this driving method will be referred to as the“three-dividing-point equal driving method”.

To set three original driving points such that points farthest from therespective original driving points within the range in which skew is tobe suppressed are equally distributed, the distance between each pointfarthest from the corresponding original driving point is set to be ⅙ ofthe total length of the control line as shown in FIG. 7.

In this case, if the total line resistance is denoted as R and the totalparasitic capacitance is denoted as C, the line resistance and theparasitic capacitance at the points farthest from the respectiveoriginal driving points are respectively given by R/6 and C/6, and thusthe time constant τd in the “three-dividing-point equal driving method”is given by equation (4). From equation (5), it can be seen that thetime constant τd is 1/9 of that in the both-end driving method and 1/36of that in the one-end driving method.[Formula 4]τd=R/6×C/6=RC/36  (4)

That is, when the “three-dividing-point equal driving method” isemployed, the theoretical skew is reduced to 1/36 of that in the one-enddriving method shown in FIG. 4 and to 1/9 of that in the both-enddriving method shown in FIG. 5.

As described above, in the first and second embodiments, two ends of thecontrol line are not used as original driving points, but a plurality oforiginal driving points are set such that points farthest from therespective original driving points within the range in which skew is tobe suppressed are equally distributed. As can be seen from these twoembodiments, the skew can be more reduced as the number of dividingpoints increases.

When the control line is driven at only one dividing point, the skewbecomes equal to that which occurs when the control line is driven atboth ends thereof. However, even in this case, the dividing-pointdriving method has the advantage that skew similar to that which occurswhen the control line is driven at both ends using two driving bufferscan be obtained using only one driving buffer.

Third Embodiment

FIG. 8 shows a skew reduction layout technique according to a thirdembodiment of the invention. In this third embodiment, in addition tothree original driving points on the control line two of which arelocated at points whose distance from a closer end of the control lineis ¼ of the total length of the control line and the other one of whichis located at the center of the control line, original driving pointsare set at two respective end points of the control line. Hereinafter,this driving method will be referred to as the “both-end andthree-dividing-point equal driving method”.

In this case, as shown in FIG. 8, if the total line resistance isdenoted as R and the total parasitic capacitance is denoted as C, theline resistance and the parasitic capacitance at the points farthestfrom the respective original driving points are respectively given byR/8 and C/8, and thus the time constant τe in the “both-end andthree-dividing-point equal driving method” is given by equation (5).From equation (5), it can be seen that the time constant τe is 1/16 ofthat in the both-end driving method and 1/64 of that in the one-enddriving method.[Formula 5]τd=R/8×C/8=RC/64  (5)

That is, when the “both-end and three-dividing-point equal drivingmethod” is employed, the theoretical skew is reduced to 1/64 of that inthe one-end driving method shown in FIG. 4 and to 1/16 of that in theboth-end driving method shown in FIG. 5. It can be seen from comparisonwith the “three-dividing-point equal driving method” according to thesecond embodiment that driving the control line not only at end pointsbut also at dividing points can reduce the delay in a central range.

Although in this third embodiment, original driving points are set atthree dividing points on the control line, two of which are located atpoints whose distance from a closer end of the control line is ¼ of thetotal length of the control line and the other one of which is locatedat the center of the control line in addition to two original drivingpoints set at two respective end points of the control line, the numberof dividing points on the control line used as original driving pointsis not limited to three, but original driving points may be set at anarbitrary number of dividing points.

Whether one or both ends are used as original driving points and/or howmany dividing points are used as original driving points may be properlydetermined depending on the number of pixels, the required responsespeed, the load resistance, the load capacitance, etc. In addition tothe main control line, one or more auxiliary control lines may be usedto drive pixels in a range that should be driven with less skew.

When the line resistance and the load capacitance are uniformlydistributed, it is desirable to set original driving points such thatpoints farthest from the respective original driving points within therange in which skew is to be suppressed are equally (symmetrically)distributed.

However, original driving points may be set such that farthest pointsare unequally distributed. Even in this case, if the positions of theoriginal driving points are selected such that a product of the lineresistance and the line capacitance (the time constant) becomes equalfor all farthest points, it is possible to achieve a similar reductionin skew to that achieved when the original driving points are set suchthat the farthest points are equally distributed (refer to a fourthembodiment described later).

For example, when a original driving point is set at one dividing pointin addition to both end points, the position of the dividing point isset such that the distance the original driving point to a pointfarthest from the original driving point is ¼ of the total length of thecontrol line. To this end, the location of the dividing point is set tobe the center of the control line. That is, two control lines areprepared one of which is connected to all pixels in a line and the otherone of which is connected to only pixels in a central range. The controlline connected only to pixels in the central range has small loadcapacitance originating from the capacitance of the pixel transistorsacting as loads, and thus driving pulses applied to this control linecan rise more steeply than those applied to the control line connectedto all pixels. The rising time can be as small as that of driving pulsesoutput from driving buffers that drives a control line at both endpoints thereof.

Instead of using both end points and one or more dividing points asoriginal driving points, only one end point and one or more dividingpoints may be used as original driving points. For example, when onlyone end point and one dividing point are used as original drivingpoints, the location of the dividing point is set such that the distancebetween the dividing point and the end point that is not selected as theoriginal driving point is equal to ⅓ of the total length of the controlline.

Fourth Embodiment

FIG. 9 shows a skew reduction layout technique according to a fourthembodiment of the invention. In this fourth embodiment, two ends of thecontrol line are not used as original driving points, but originaldriving points are set at dividing points on the control line such thatpoints farthest from original driving points are distributed at unequalintervals and such that a product of the line resistance and the linecapacitance (the time constant) becomes equal for all farthest points.Hereinafter, this driving method will be referred to as an “unequaldriving method”.

When the line resistance and the line capacitance are distributednon-uniformly, if driving buffers are disposed at locations that causethe time constant τf given by a product of the line resistance and theline capacitance to be equal for all farthest points, it is possible toachieve a reduction in skew similar to that achieved according to one ofthe first to third embodiments.

For example, when original driving points are set at two unsymmetricalpoints, the time constant τf for any furthest point (at which the timeconstant becomes greatest) is given by equation (6). From equation (6),it can be seen that the time constant τf is 1/9 of that in the both-enddriving method and 1/36 of that in the one-end driving method.[Formula 6]τf=16RC/(27×27)=16RC/729  (6)

Thus, if the “unequal driving method” according to the fourth embodimentof the invention is employed, the theoretical skew can be reduced to16/729 of that in the one-end driving method shown in FIG. 4 and to4/729 of that in the both-end driving method shown in FIG. 5.

As described above, in the present invention, a control line within arange in which skew is to be suppressed is driven at least at one ormore arbitrary dividing points (driving at a plurality of dividingpoints is more desirable than driving at one dividing point) such thatskew is reduced in the range in which skew is to be suppressed.

When line resistance and load capacitance of a control line areuniformly distributed, and when the number of driving buffers fordriving the control line at dividing points is given, if the locationsof the dividing points are set such that points farthest from therespective original driving points connected to the driving buffers arelocated at uniform intervals on the control line, this arrangementminimizes the maximum value of the product of the line resistance andthe load capacitance between an arbitrary driving point on the controlline and a driving buffer within the effective range in which the skewis to be suppressed.

When line resistance and load capacitance of a control line arenon-uniformly distributed, and when the number of driving buffers fordriving the control line at dividing points is given, if the locationsof the dividing points are set such that the time constant becomes equal(and preferably greatest) at any point farthest from the respectiveoriginal driving points connected to the driving buffers, it is possibleto achieve a greatest improvement in skew.

In the present invention, because a control line is driven at a dividingpoint on the control line, skew can be reduced in a range in which skewshould be suppressed, by using a small number of driving circuits.

If the location of the dividing point is determined such that thelocation results in a reduction in the maximum value of the timeconstant given by the product of load capacitance at an arbitrarydriving point on the control line and line resistance between thearbitrary driving point and a driver unit that drives the originaldriving point, then it becomes possible to drive the control line at anoptimum position even when the line resistance and the load capacitanceare distributed non-uniformly.

Thus, the present invention makes it possible to ease a problem (skew)caused by non-uniformity of the driving capacity, which is very seriousin particular when the number of pixels is increased or when pixels aredriven at a high speed. Thus, it is possible to reduce shading and otherproblems.

CMOS image sensor is used as an example of a semiconductor device thepresent invention to which the present invention is applied. Also thisinvention is applied to a physical information acquisition apparatuslike a camera module or a camera.

What is claimed is:
 1. A physical information acquisition apparatuscomprising: a semiconductor device including a plurality of pixelelements arranged in a particular order, each pixel element having asignal generation part for outputting at least one signal indicating adetected change in a physical quantity; and a drive control unit thatdrives a control line at a point located on the control line such that amaximum value of a product of (a) load capacitance at an arbitrarydriving point on the control line and (b) line resistance between thearbitrary driving point and a driver unit that is connected to the pointis substantially a local minimum, wherein the point is at a positionalong the driving control line between the ends of the control line andthe control line is connected to at least one of the plurality of pixelelements.
 2. A physical information acquisition apparatus according toclaim 1, wherein the drive control unit is disposed in the semiconductordevice.
 3. The physical information acquisition apparatus according toclaim 1, wherein the drive control unit causes a drive control pulse tobe provided from the driver unit at a same timing as that of a drivecontrol pulse supplied from one or both end points of the control line.4. The physical information acquisition apparatus according to claim 1,wherein the drive control unit causes a drive control pulse to beprovided from the driver unit at a same timing as that of a drivecontrol pulse supplied from another point on the control line.
 5. Thephysical information acquisition apparatus according to claim 1, whereinthe drive control unit drives the control line at a point located on thecontrol line such that a maximum value of a product of (a) loadcapacitance at an arbitrary driving point on the control line and (b)line resistance between the arbitrary driving point and the driver unitthat is connected to the point is substantially a local minimum.
 6. Thephysical information acquisition apparatus according to claim 1, whereinthe drive control unit drives one or more other points located on thecontrol line.
 7. The physical information acquisition apparatusaccording to claim 6, wherein the point and the one or more other pointsare equally distributed on the control line.
 8. The physical informationacquisition apparatus according to claim 6, wherein the point and theone or more other points are unequally distributed on the control line.9. The physical information acquisition apparatus according to claim 1,wherein the drive control unit drives another control line at a pointlocated on the another control line.
 10. The physical informationacquisition apparatus according to claim 9, wherein the another controlline is connected to all pixels in a line.
 11. The physical informationacquisition apparatus according to claim 1, wherein the drive controlpulse is provided to the point at a same timing as that of a drivecontrol pulse supplied provided from one or both end points of thecontrol line.
 12. The physical information acquisition apparatusaccording to claim 1, wherein the drive control pulse is provided to thepoint at a same timing as that of a drive control pulse suppliedprovided from another point on the control line.